1. Field of the Invention
The present invention relates to a method and an apparatus for combustion harmfulness-elimination of PFC (perfluoro-compound) gas. More particularly, the invention relates to a method and an apparatus for eliminating the noxious substances of PFC gas through combustion, which prevent or effectively suppress the corrosion in the apparatus and the generation of byproducts due to combustion of PFC gas, thereby reducing the number of cleaning and/or part-exchange operations for the apparatus.
2. Description of the Related Art
In the fabrication process sequence of semiconductor devices, dry etching apparatuses are frequently used. In such the dry etching process for semiconductor device fabrication, a PFC gas such as sulfur hexafluoride SF6) and trifluoromethane (CHF3) is often supplied to the dry etching apparatus in the form of gaseous mixture consisting of a PFC gas and a chlorine (Cl)-based gas or a carrier gas such as helium (He).
PFC gasses are generally harmful and therefore, they are usually subjected to a combustion harmfulness-elimination process prior to discharge or release to the atmosphere, in other words, they are contacted with flames to decompose the harmful constituent(s) to unharmful substance(s).
For example, the Japanese Non-Examined Patent Publication No. 10-249 143 published in 1998 discloses a method of treating a waste gas using the combustion harmfulness-elimination process. In this method, a waste gas to be treated (e.g., a gas containing silane (SiH4) and at least one volatile inorganic hydrogen compound, such as arsine (AsH3), phosphine (PH3), and diborane (B2H6) is contacted with flames for eliminating its harmfulness.
FIG. 1 schematically shows a conventional apparatus 50 for combustion harmfulness-elimination of PFC gas, which comprises a wet scrubber 52, a gas introduction section 56, a combustion furnace 57, and a combustion control section 58.
An introduction pipe 51 is connected to the inlet of the scrubber 52. A first gaseous mixture M1 is introduced into the apparatus 50 and sent to the inlet of the scrubber 52 by way of the pipe 51. The outlet of the scrubber 52 is connected to the inlet of the gas introduction section 56 by way of connection pipes 53 and 55.
An introduction pipe 54 is connected to the connection point of the pipes 53 and 55. A second gaseous mixture M2 is introduced into the apparatus 50 and sent to the inlet of the section 56 by way of the pipes 54 and 55. The gas introduction section 56 is connected to the combustion control section 58. The combustion control section 58 is connected to the combustion furnace 57. The combustion control section 58 has a combustion gas introduction section 59 for introducing a combustion gas CG into the section 58.
The combustion control section 58 controls the combustion or burning state in the furnace 57. In other words, the section 58 generates flames 60 by burning the combustion gas CG introduced by way of the section 59, and eliminates the flames 60, according to the necessity.
The furnace 57 has an air introduction section 61 and an outlet or exhaust port 62. The air introduction section 61 is used to introduce the air for diluting the gaseous compound generated in the furnace 57 by the combustion harmfulness-elimination process as the diluting air DA. The outlet port 62 is used to discharge the diluted gaseous compound in the furnace 57 into the atmosphere as an exhaust gas EX.
On operation, for example, a mixture of a PFC gas (e.g., SF6 or CHF3) and a Cl-based gas as the first gaseous mixture M1 is introduced into the apparatus 50 and sent to the scrubber 52 by way of the pipe 51. The Cl-based gas contained in the mixture M1 is removed in the scrubber 52 by wet scrubbing treatment, resulting in a processed mixture M1′ containing the PFC gas. The processed mixture M1′ is sent to the gas introduction section 56 by way of the pipes 53 and 55.
On the other hand, a mixture of the same PFC gas as the first mixture M1 and He gas as its carrier, which is the second gaseous mixture M2, is introduced into the apparatus 50 through the pipe 54. Then, the mixture M2 is sent to the gas introduction section 56 by way of the pipe 55.
The PFC gas contained in the processed mixture M1 and the second mixture M2, which has been sent to the gas introduction section 56, is then sent to the inside of the combustion furnace 57 where the flames 60 are formed. The flames 60 are generated by burning the combustion gas CG introduced through the section 59 under the control of the section 59. In the furnace 57, the PFC gas contained in the mixtures M1 and M2 is burnt and decomposed to unharmful or less-harmful gaseous substances. The unharmful or less-harmful substances thus generated are diluted by the air DA introduced through the section 61 and then, discharged from the furnace 57 by way of the outlet or exhaust port 62 as an exhaust gas EX.
With the conventional apparatus 50, there is a problem that byproducts are generated and deposited onto the inner walls of the combustion control section 58 after approximately one month's use, which induces the insufficient combustion efficiency. Thus, the inside of the apparatus 50 needs to be cleaned once approximately per month. Moreover, there is another problem that corrosion occurs on the inner walls of the gas introduction section 56.